1. Field of the Invention
The present invention relates generally to the art of preventing environmental pollution attributable to the exhaust gas of internal combustion engines or the like.
Particularly, the present invention concerns an improvement in an exhaust gas filter for removing particulates such as soot, which is inevitably contained in the exhaust gas of a diesel engine.
2. Description of Prior Art
Particulates such as soot contained in the exhaust gas of diesel engines have recently been reported to be carcinogenic and it is therefore desirable to eliminate such particles from exhaust gases. Although combustors and engines are being improved in order to reduce the emission of such particulates, for the present time it is considered best to trap the particulates with a filter and then burn the particulates trapped on the filter. Various methods have been proposed for eliminating the particulates in exhaust gases.
Conventional proposals include metal mesh or ceramic fibers packed and sealed in a container as a filter element. Porous ceramic foams or extruded ceramic honeycombs are also used. Devices using a metal mesh or packed ceramic fiber randomly filled as the filler element are apt to blow off the fibers, particularly ceramic fibers, during operation resulting in poor filtration. The metal mesh may encounter a problem of melting down during regenerating the filtering function in which the trapped particulates are burnt. The ceramic foam and the extruded ceramic honeycomb often have insufficient thermal shock resistance. The extruded ceramic honeycomb has an insufficient gas permeability which causes a large pressure drop, because it cannot be structured to have a large porosity.